This invention relates to diplexers for separating electromagnetic signals at different spectral regions from a common port of the diplexer as well as for combining the signals at the common port and, more particularly, for operation as a multiplexer of signals disposed in spectral regions two of which are separated by at least approximately one octave in frequency and wherein the signals have a common polarization.
Diplexers are frequently used in communication systems for separating two signal channels, such as a received signal channel and a transmitted signal channel, wherein the two channels differ in frequency but are sufficiently close in frequency to fall within the same region of the electromagnetic spectrum. For example, the two channels may carry C-band signals, approximately 5 GHz (gigahertz), or two X-band signals, approximately 10 GHz. A typical situation for a diplexer is the connection of a single antenna to a transmitter and a receiver operating at different frequencies. Generally, the operation of a diplexer is reciprocal so that the diplexer can be used also to combine two signal channels.
In satellite communications, a satellite may carry a number of receivers and transmitters for reception of up link signals and transmission of down link signals in the manner of a relay station. The up link and the down link signals differ in frequency. Often a transmitter and a receiver share a common antenna, with connection to the antenna being made by means of a diplexer. A situation of considerable interest arises when it is desirable to employ a common antenna or communication link not only with signal channels in a first portion of the spectrum, but also with a further signal channel lying in a second portion of the spectrum differing in frequency from the first portion by an octave or more. A case in point is the situation wherein it is desired to employ both Ku band and C band signals with a common antenna. A problem arises in that a diplexer suitable for accomplishing the foregoing multiplexing of signals has not been available.